Cooling and air flow exhaust for image projection apparatus

ABSTRACT

An image projection apparatus is disclosed which is capable of reducing noise when airflows from plural flow paths are taken in into a fan and exhausted therefrom. The apparatus comprises a first flow path through which a first airflow for cooling a light source passes, a second flow path through which a second airflow for cooling constituent parts other than the light source passes, a fan which exhausts air introduced from the first and second flow paths to the outside of the apparatus, a third flow path which introduces a third airflow to an exhaust area between the light source and the fan in the first flow path, and a light-shielding member which is provided in the exhaust area and shields the light from the light source.

BACKGROUND OF THE INVENTION

The present invention relates to an image projection apparatus, such asa liquid crystal projector, which is provided with a cooling fan.

Projector is provided with heat-generating parts which are opticalsystem parts including a light source, light modulation elements such asliquid crystal panels and optical elements, and electrical system partsincluding a light source ballast and a CPU.

To appropriately cool these heat-generating parts, the cooling methoddisclosed in Japanese Patent Laid-Open No. 2000-19496 uses plural fans.In this method, plural flow paths are formed in accordance with heatvalues of the heat-generating parts, such as a flow path for cooling alight source, a flow path for cooling a light modulation element and aflow path for cooling a light source ballast. The cooling airflows thatpassed through the flow paths are finally combined and exhausted by afan.

This achieves cooling with high efficiency by using the minimum numberof fans to reduce the size of the projector. Furthermore, this candecrease the number of exhaust openings through which noise generatedinside the apparatus leaks. This may achieve a low-noise projector.

However, in such a configuration in which plural airflows flow into onefan from plural flow paths, when the plural airflows have greatlydifferent flow velocities, noise generated in the fan is increased.

This phenomenon will be described using FIG. 7. FIG. 7 shows thephenomenon of generation of noise in an axial flow fan.

In this figure, reference numeral 18F denotes the axial flow fan.Reference symbol WA denotes an airflow which is taken in into the axialflow fan 18F from a first flow path. Reference symbol WB denotes anairflow which is taken in into the axial flow fan 18F from a second flowpath. Reference numeral 18Fa denotes the leading edge of a blade of theaxial flow fan 18F in its rotation direction.

The airflow WB has a velocity much higher than that of the airflow WA.In this case, the leading edge 18Fa of the blade perpendicularly cutseach airflow when the fan 18F is rotated. The leading edge 18Fa of theblade hits the side face of the airflow WB when the leading edge 18Fathat was cutting the slow airflow WA starts to cut the fast airflow WB,which generates wind noise. This wind noise is peaked at a frequency ofan integral multiple of ‘the number of the blades×the rotation speedthereof’, which causes noise.

In addition, the leading edge 18Fa of the rotating blade forms differentangles of attack with respect to the airflows WA and WB which havedifferent velocities. The airflow WB providing a larger angle of attackbecomes burble on the surface of the blade, which causes turbulent flownoise.

A conventional art is known, as disclosed in Japanese Patent Laid-OpenNo. H11-82393, in which an airflow is uniformly introduced to a fan toallow the airflow to be uniformly blown to a heat-generating part,thereby carrying out cooling with good efficiency.

The art disclosed in Japanese Patent Laid-Open No. H11-82393, however,is an art for a case of a single airflow and an art focused on the flowvolume distribution on the blowout side of the fan. In other words, theart does not aim to reduce noise when plural airflows are taken in intoone fan.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an image projection apparatus capable offurther reducing noise when airflows from plural flow paths are taken ininto a fan and exhausted therefrom.

According to an aspect, the present invention provides an imageprojection apparatus which projects an image using light from a lightsource. The apparatus comprises a first flow path through which a firstairflow for cooling the light source passes, a second flow path throughwhich a second airflow for cooling constituent parts other than thelight source passes, a fan which exhausts air introduced from the firstand second flow paths to the outside of the apparatus, a third flow pathwhich introduces a third airflow to an exhaust area between the lightsource and the fan in the first flow path, and a light-shielding memberwhich is provided in the exhaust area and shields the light from thelight source.

According to another aspect, the present invention provides an imagedisplay system which comprises the abovedescribed image projectionapparatus and an image supply apparatus which supplies image informationto the image projection apparatus.

Other objects and features of the present invention will be apparentfrom the following description of preferred embodiments with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plane view showing part of the cooling structure in theliquid crystal projector that is Embodiment 1 of the present invention.

FIG. 2 is a perspective view showing part of the cooling structure inEmbodiment 1.

FIG. 3 is a plane view showing part of the cooling structure in theliquid crystal projector that is Embodiment 2 of the present invention.

FIG. 4 is an exploded perspective view showing the overall configurationof the liquid crystal projector of Embodiment 1.

FIGS. 5A and 5B are a plane view and a side view, respectively, showingthe optical configuration in the liquid crystal projector of Embodiment1.

FIG. 6 is a plane view showing airflows in the liquid crystal projectorof Embodiment 1.

FIG. 7 is an illustration for explaining generation of wind noise.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed with reference to the drawings.

Embodiment 1

(Overall Configuration of Projector)

FIG. 4 shows the configuration of the liquid crystal projector (imageprojection apparatus) that is Embodiment 1 of the present invention.

In this figure, reference numeral 1 denotes a light source lamp, 2 alamp holder which holds the lamp 1, 3 an explosion-proof glass, and 4 aglass holder. Reference symbol a denotes an illumination optical systemwhich converts light from the lamp 1 into uniform and parallel light.Reference symbol β denotes a color separation/combination opticalsystem. The color separation/combination optical system β separates thelight from the lamp 1 into a red (R) light component, a green (G) lightcomponent and a blue (B) light component, guides them to liquid crystalpanels for R, G, and B, respectively, and then combines the lightcomponents from the liquid crystal panels.

Reference numeral 5 denotes a projection lens barrel which projectslight from the color separation/combination optical system β onto ascreen (projection surface), not shown. A projection optical system ishoused in the projection lens barrel 5.

Reference numeral 6 denotes an optical box which houses the lamp 1, theillumination optical system α and the color separation/combinationoptical system β, and to which the projection lens barrel 5 is fixed.The optical box 6 has a lamp case portion formed thereon, whichsurrounds the lamp 1.

Reference numeral 7 denotes an optical box lid which covers the opticalbox 6 housing the illumination optical system α and the colorseparation/combination optical system β. Reference numeral 8 denotes aPFC (Power Factor Correction) power supply board which generates DCpower for each of circuit boards from a commercial power source, 9 apower supply filter board, and 10 a ballast power supply board whichdrives (lights) the lamp 1 together with the PFC power supply board 8.

Reference numeral 11 denotes a control board which drives the liquidcrystal panels and controls lighting of the lamp 1 with power from thePFC power supply board 8.

Reference numerals 12A and 12B denote first and second optical systemcooling fans, respectively, which take in air through an air intake port21 a formed in a lower exterior case 21, later described, to cooloptical elements such as the liquid crystal panels and polarizing platesprovided in the color separation/combination optical system β. Referencenumeral 13 denotes a first RGB duct which guides the cooling airflowsfrom the first and second optical system cooing fans 12A and 12B to theoptical elements in the color separation/combination optical system β.

Reference numeral 14 denotes a lamp cooling fan which sends the blowingairflow to the lamp 1 to cool it. Reference numeral 15 denotes a firstlamp duct which holds the lamp cooling fan 14 and guides the coolingairflow to the lamp 1. Reference numeral 16 denotes a second lamp ductwhich holds the lamp cooling fan 14 and forms the duct together with thefirst lamp duct 15.

Reference numeral 17 denotes a power source cooing fan which takes inair through an air intake port 21 b formed in the lower exterior case 21to circulate a cooling airflow within the PFC power supply board 8 andthe ballast power supply board 10 to cool them. Reference numeral 18denotes an exhaust fan which exhausts air that was provided from thelamp cooling fan 14 to the lamp 1 and whose temperature is increased bycooling the lamp 1 through an exhaust port 24 a formed in a second sideplate 24, later described.

Reference numeral 19 denotes a first exhaust louver and 20 a secondexhaust louver, both of which allows passage of the exhaust air and havea light shielding function to prevent leakage of light from the lamp 1to the outside of the projector.

The lower exterior case 21 houses the lamp 1, the optical box 6, thelight source system boards 8 to 10, the control board 11 and the like.

Reference numeral 22 denotes an upper exterior case which covers thelower exterior case 21 housing the optical box 6 and the like. Referencenumeral 23 denotes a first side plate which covers side openings formedby the cases 21 and 22 together with the second side plate 24. The lowerexterior case 21 has the abovementioned air intake ports 21 a and 21 bformed therein, and the side plate 24 has the exhaust port 24 a formedtherein. The lower exterior case 21, the upper exterior case 22, thefirst side plate 23 and the second side plate 24 constitute the chassis(case) of the projector.

Reference numeral 25 denotes an interface board on which connectors forreceiving various signals are mounted, and 26 an interface reinforcementplate attached to the inside face of the first side plate 23.

Reference numeral 27 denotes an exhaust box which guides the exhaust airfrom the lamp 1 to the exhaust fan 18 to prevent diffusion of theexhaust air in the chassis. The exhaust box 27 holds the first andsecond exhaust louvers 19 and 20.

Reference numeral 28 denotes a lamp lid. The lamp lid 28 is removablyprovided on the bottom of the lower exterior case 21 and is fixedthereto by screws, not shown. Reference numeral 29 denotes a setadjustment leg. The set adjustment leg 29 is fixed to the lower exteriorcase 21, and the height of its leg 29 a can be adjustable. Theadjustment of the height of the leg 29 a enables adjustment of theinclination angle of the projector.

Reference numeral 30 denotes an RGB air intake plate which holds afilter, not shown, attached to the outside of the air intake port 21 aformed in the lower exterior case 21.

Reference numeral 31 denotes a prism base which holds the colorseparation/combination optical system β. Reference numeral 32 denotes abox side cover which has duct-shaped portions for guiding the coolingairflows from the first and second cooling fans 12A and 12B for coolingthe optical elements (including the liquid crystal panels) in the colorseparation/combination optical system β. Reference numeral 33 denotes asecond RGB duct which forms the duct together with the box side cover32.

Reference numeral 34 denotes an RGB board to which a flexible boardextending from the liquid crystal panels disposed in the colorseparation/combination optical system β is connected and which isconnected to the control board 11.

(Optical Configuration)

Next, description will be made of the configuration of the entireoptical system formed of the abovementioned lamp 1, the illuminationoptical system α, the color separation/combination optical system β andthe projection lens barrel (projection optical system) 5 with referenceto FIGS. 5A and 5B. FIG. 5A shows a horizontal section of the opticalsystem, and FIG. 5B shows a vertical section thereof.

In these figures, reference numeral 41 denotes a light-emitting tubewhich emits white light in a continuous spectrum, and 42 a reflectorwhich collects light from the light-emitting tube 41 in a predetermineddirection. The light-emitting tube 41 and the reflector 42 constitutethe lamp 1.

Reference numeral 43 a denotes a first cylinder array which is formed byarranging plural cylindrical lens cells each having a refractive powerin a horizontal direction shown in FIG. 5A, 43 b a second cylinder arraywhich has plural cylindrical lens cells corresponding to the respectivelens cells of the first cylinder array 43 a. Reference numeral 44denotes an ultraviolet absorbing filter, and 45 a polarizationconversion element which converts non-polarized light into polarizedlight having a predetermined polarization direction.

Reference numeral 46 denotes a front compressor which is formed of acylindrical lens having a refractive power in a vertical direction shownin FIG. 5B. Reference numeral 47 denotes a reflecting mirror which bendsthe optical axis from the lamp 1 by 90 degrees (in more detail, by 88degrees).

Reference numeral 43 c denotes a third cylinder array which is formed byarranging plural cylindrical lens cells each having a refractive powerin the vertical direction. Reference numeral 43 d denotes a fourthcylinder array which has plural cylindrical lens cells corresponding tothe respective lens cells of the third cylinder array 43 c.

Reference numeral 50 denotes a color filter which returns color light ina specific wavelength range to the lamp 1 for adjustment of colorcoordinates to predetermined values. Reference numeral 48 denotes acondenser lens. Reference numeral 49 denotes a rear compressor which isformed of a cylindrical lens having a refractive power in the verticaldirection. The abovementioned components constitute the illuminationoptical system α.

Reference numeral 58 denotes a dichroic mirror which reflects light inthe wavelength ranges of blue (B: for example, 430 nm to 495 nm) and red(R: for example, 590 nm to 650 nm) and transmits light in the wavelengthrange of green (G: for example, 505 nm to 580 nm). Reference numeral 59denotes an entrance-side polarizing plate for G which includes apolarizing element attached on a transparent substrate and transmitsonly P-polarized light. Reference numeral 60 denotes a firstpolarization beam splitter which has a polarization beam splittingsurface transmitting P-polarized light and reflecting S-polarized light.

Reference numerals 61R, 61G and 61B denote a reflective liquid crystalpanel for R, a reflective liquid crystal panel for G and a reflectiveliquid crystal panel for B, respectively, each being a light modulationelement (or image forming element) which reflects and image-modulatesentering light. Reference numerals 62R, 62G and 62B denote aquarter-wave plate for R, a quarter-wave plate for G and a quarter-waveplate for B, respectively.

Reference numeral 64 a denotes a trimming filter which returns orangelight to the lamp 1 for enhancing the color purity of red. Referencenumeral 64 b denotes an entrance-side polarizing plate for R and B whichincludes a polarizing element attached on a transparent substrate andtransmits only P-polarized light.

Reference numeral 65 denotes a color-selective phase plate whichconverts the polarization direction of red light by 90 degrees and doesnot convert the polarization direction of blue light. Reference numeral66 denotes a second polarization beam splitter which has a polarizationbeam splitting surface transmitting p-polarized light and reflectingS-polarized light.

Reference numeral 68B denotes an emergence-side polarizing plate for Bwhich transmits only the S-polarized light component of B light.Reference numeral 68G denotes an emergence-side polarizing plate for Gwhich transmits only S-polarized light of G light. Reference numeral 69shows a dichroic prism which transmits R light and B light, and reflectsG light.

The abovementioned components from the dichroic mirror 58 to thedichroic prism 69 constitute the color separation/combination opticalsystem β.

In this embodiment, the polarization conversion element 45 convertsP-polarized light into S-polarized light. The P-polarized light andS-polarized light are herein described relative to the polarizationdirection of light at the polarization conversion element 45. On theother hand, the light entering the dichroic mirror 58 is consideredrelative to the polarization direction at the first and secondpolarization beam splitters 60 and 66, the light being regarded asP-polarized light. While the light emerging from the polarizationconversion element 45 is S-polarized light, the S-polarized light isdefined as P-polarized light when it enters the dichroic mirror 58.

Next, the optical effects will be described.

The light emitted from the light-emitting tube 41 is collected in apredetermined direction by the reflector 42. The reflector 42 has aparaboloidal shape, and the luminous flux from the focal point of theparaboloidal surface is converted into a luminous flux parallel to theaxis of symmetry of the paraboloidal surface. However, since the lightsource in the light-emitting tube 41 is not an ideal point light sourceand has a finite size, the collected luminous flux contains a largeamount of light component not in parallel with the axis of symmetry ofthe paraboloidal surface.

The luminous flux enters the first cylinder array 43 a through theexplosion-proof glass 3. The luminous flux entering the first cylinderarray 43 a is divided into plural luminous fluxes in accordance with thenumber of the cylindrical lens cells thereof and collected thereby toform plural luminous fluxes each of which has a band-like shape andwhich are arranged in the vertical direction. These luminous fluxes arepassed through the ultraviolet absorbing filter 44 and the secondcylinder array 43 b and then form plural images of the light source nearthe polarization conversion element 45.

The polarization conversion element 45 is constituted by polarizationbeam splitting surfaces, reflecting surfaces, and half-wave plates. Eachof the luminous fluxes enters the polarization beam splitting surfacecorresponding to its row and is separated into a P-polarized lightcomponent which is transmitted through the polarization beam splittingsurface and an S-polarized light component which is reflected thereby.

The reflected S-polarized light component is reflected by the reflectingsurface and then emerges in the same direction as the P-polarized lightcomponent. On the other hand, the transmitted P-polarized lightcomponent is transmitted through the half-wave plate to be convertedinto the same polarized light component as the S-polarized lightcomponent. Thus, the polarized luminous fluxes which are polarized inthe same direction emerge from the polarization conversion element 45.

The plural luminous fluxes converted into the polarized luminous fluxesby the polarization conversion element 45 are compressed by the frontcompressor 46, reflected by the reflecting mirror 47 by 90 (88) degreesand then enter the third cylinder array 43 c.

Each of the luminous flux entering the third cylinder array 43 c isdivided into plural luminous fluxes in accordance with the number of thecylindrical lens cells thereof and collected thereby to form pluralluminous fluxes each of which has a band-like shape and which arearranged in the horizontal direction. The plural luminous fluxes arepassed through the fourth cylinder array 43 d and the condenser lens 48and then enter the rear compressor 49.

With the optical actions of the front compressor 46, the condenser lens48 and the rear compressor 49, rectangular images formed by the pluralluminous fluxes are overlapped with each other to form a rectangularillumination area with a uniform brightness. Each of the reflectiveliquid crystal panels 61R, 61G and 61B is disposed in the illuminationarea.

The S-polarized light converted by the polarization conversion element45 impinges on the dichroic mirror 58. The optical path of the G lighttransmitted through the dichroic mirror 58 will hereinafter bedescribed.

The G light transmitted through the dichroic mirror 58 enters theentrance-side polarizing plate 59. The G light remains as P-polarizedlight (S-polarized light relative to the polarizing conversion element45) after the separation by the dichroic mirror 58. The G light emergesfrom the entrance-side polarizing plate 59, enters the firstpolarization beam splitter 60 as P-polarized light and then istransmitted through the polarization beam splitting surface thereof toreach the reflective liquid crystal panel 61G.

An image supply apparatus 80 such as a personal computer, DVD player,VCR and a television tuner is connected to the IF board 25 of theprojector. The control circuit 11 drives the reflective liquid crystalpanels 61R, 61G and 61B based on image (video) information input fromthe image supply apparatus 80 and causes them to form original imagesfor the respective colors. Thus, the light entering each reflectiveliquid crystal panel is modulated (image-modulated) in accordance withthe original image and reflected thereby. The projector and the imagesupply apparatus 80 constitute an image display system.

The reflective liquid crystal panel 61G image-modulates the G light andreflects it. The P-polarized light component of the image-modulated Glight is again transmitted through the polarization beam splittingsurface of the first polarization beam splitter 60 and thereby returnedtoward the light source to be removed from light for projection. On theother hand, the S-polarized light component of the image-modulated Glight is reflected by the polarization beam splitting surface of thefirst polarization beam splitter 60 to be directed toward the dichroicprism 69 as light for projection.

In a state in which all the polarized light components are convertedinto P-polarized light (in a black display state), adjusting the slowaxis of the quarter-wave plate 62G provided between the firstpolarization beam splitter 60 and the reflective liquid crystal panel61G to a predetermined direction can reduce the influence of adisturbance of the polarization state caused in the first polarizationbeam splitter 60 and the reflective liquid crystal panel 61G.

The G light that emerged from the first polarization beam splitter 60enters the dichroic prism 69 as S-polarized light and then is reflectedby the dichroic film surface of the dichroic prism 69 to reach theprojection lens barrel 5.

On the other hand, the R light and B light reflected by the dichroicmirror 58 enter the trimming filter 64 a. The R light and the B lightremain as P-polarized light after the separation by the dichroic mirror58. The R light and the B light are passed through the trimming filter64 a to remove the orange light component thereof, transmitted throughthe entrance-side polarizing plate 64 b and then enter thecolor-selective phase plate 65.

The color-selective phase plate 65 has a function of rotating thepolarization direction of only R light by 90 degrees. Thus, the R lightand the B light enter the second light beam splitter 66 as S-polarizedlight and P-polarized light, respectively.

The R light entering the second polarization beam splitter 66 asS-polarized light is reflected by the polarization beam splittingsurface of the second polarization beam splitter 66 to reach thereflective liquid crystal panel 61R. The B light entering the secondpolarization beam splitter 66 as P-polarized light is transmittedthrough the polarization beam splitting surface of the secondpolarization beam splitter 66 to reach the reflective liquid crystalpanel 61B.

The R light entering the reflective liquid crystal panel 61R isimage-modulated and reflected thereby. The S-polarized light componentof the image-modulated R light is reflected again by the polarizationbeam splitting surface of the second polarization beam splitter 66 andthereby returned toward the light source to be removed from light forprojection. On the other hand, the P-polarized light component of theimage-modulated R light is transmitted through the polarization beamsplitting surface of the second polarization beam splitter 66 to bedirected toward the dichroic prism 69 as light for projection.

The B light entering the reflective liquid crystal panel 61B isimage-modulated and reflected thereby. The P-polarized light componentof the image-modulated B light is transmitted again through thepolarization beam splitting surface of the second polarization beamsplitter 66 and thereby returned toward the light source to be removedfrom light for projection. On the other hand, the S-polarized lightcomponent of the image-modulated B light is reflected by thepolarization beam splitting surface of the second polarization beamsplitter 66 to be directed toward the dichroic prism 69 as light forprojection.

Adjusting each of the slow axes of the quarter-wave plates 62R and 62Bprovided between the second polarization beam splitter 66 and thereflective liquid crystal panels 61R and 61B, respectively, can reducethe influence of a disturbance of the polarization state in the blackdisplay state for each of the R light and the B light, as is the casefor the G light.

Of the R light and B light that are thus combined into one luminous fluxby the second polarization beam splitter 66 and then emerged therefrom,the B light is analyzed by the emergence-side polarizing plate 68B andthen enters the dichroic prism 69. The R light is transmitted throughthe polarizing plate 68B with no change as P-polarized light and thenenters the dichroic prism 69.

The analysis by the emergence-side polarizing plate 68B removesunnecessary components of the B light caused by passing the secondpolarization beam splitter 66, the reflective liquid crystal panel 61Band the quarter-wave plate 62B.

The R light and the B light for projection entering the dichroic prism69 are transmitted through the dichroic film surface of the dichroicprism 69, combined with the G light reflected by the dichroic filmsurface and then reach the projection lens barrel 5.

The combined R, G and B light for projection is enlarged and projectedby the projection optical system in the projection lens barrel 5 onto aprojection surface such as a screen.

The optical paths described above are used when the reflective liquidcrystal panels operate in a white display state. Description willhereinafter be made of optical paths when the reflective liquid crystalpanels operate in the black display state.

First, the optical path of the G light will be described. TheP-polarized light component of the G light transmitted through thedichroic mirror 58 enters the entrance-side polarizing plate 59 and thefirst polarization beam splitter 60, is transmitted through thepolarization beam splitting surface thereof and then reaches thereflective liquid crystal panel 61G. Since the reflective liquid crystalpanel 61G is in the black display state, the G light is reflectedwithout image-modulation. Thus, the G light remains as P-polarized lightafter the reflection by the reflective liquid crystal panel 61G.Therefore, the G light is again transmitted through the polarizationbeam splitting surface of the first polarization beam splitter 60 andthe entrance-side polarizing plate 59 and returned toward the lightsource to be removed from light for projection.

Next, the optical paths of the R light and B light will be described.The P-polarized light components of the R light and B light reflected bythe dichroic mirror 58 enter the entrance-side polarizing plate 64 b.They emerge from the entrance-side polarizing plate 64 b and then enterthe color-selective phase plate 65. Since the color-selective phaseplate 65 has the function of rotating the polarization direction of onlythe R light by 90 degrees, the R light and the B light enter the secondbeam splitter 66 as S-polarized light and P-polarized light,respectively.

The R light entering the second polarization beam splitter 66 as theS-polarized light is reflected by the polarization beam splittingsurface thereof and reaches the reflective liquid crystal panel 61R. TheB light entering the second polarization beam splitter as theP-polarized light is transmitted through the polarization beam splittingsurface thereof and reaches the reflective liquid crystal panel 61B.

Since the reflective liquid crystal panel 61R is in the black displaystate, the R light entering the reflective liquid crystal panel 61R isreflected without image-modulation. In other words, the R light remainsas the S-polarized light after the reflection by the reflective liquidcrystal panel 61R. Thus, the R light is again reflected by thepolarization beam splitting surface of the second polarization beamsplitter 66, transmitted through the entrance-side polarizing plate 64 band then returned toward the light source to be removed from light forprojection. As a result, black is displayed.

The B light entering the reflective liquid crystal panel 61B isreflected without image-modulation since the reflective liquid crystalpanel 61B is in the black display state. In other words, the B lightremains as the P-polarized light after the reflection by the reflectiveliquid crystal panel 61B. Thus, the B light is again transmitted throughthe polarization beam splitting surface of the second polarization beamsplitter 66, converted into P-polarized light by the color-selectivephase plate 65, transmitted through the entrance-side polarizing plate64 b and returned toward the light source to be removed from light forprojection.

(Cooling Structure)

Next, description will be made of the cooling structure in the projectorof the present embodiment with reference to FIG. 6. As described above,the projector houses five fans 12A, 12B, 14, 17 and 18, which provideairflows into plural flow paths to cool the following respective coolingobjects.

In a flow path B (a first flow path) shown by solid arrows in FIG. 6,the air taken in into the chassis by the lamp cooling fan 14 is providedas cooling airflow to the lamp 1 through the duct formed by the firstand second lamp ducts 15 and 16. The air that cooled the lamp 1 isguided to the exhaust box 27 to be exhausted to the outside of thechassis by the exhaust fan 18.

In a flow path A (a second flow path) shown by dotted arrows in FIG. 6,the air taken in by the first and second cooling fans 12A and 12Bthrough the air intake port 21 a formed below the projection lens barrel5 from the outside of the chassis flows thereinto. The second coolingfan 12B is disposed below the projection lens barrel 5.

The cooling airflow passing through the flow path A cools the opticalelements in the color separation/combination optical system β housed inthe optical box 6. Most of the cooling airflow flows toward the PFCpower source board 8 and the ballast power source board 10, which aredisposed adjacent to the optical box 6, cools electrical parts mountedon the boards 8 and 10 and then is exhausted to the outside of thechassis by the exhaust fan 18 and the power source cooling fan 17.

Furthermore, in a flow path C shown by dashed-dotted arrows in FIG. 6,the air taken in through the air intake port 21 b, not shown in FIG. 6,formed in the lower exterior case 21 flows into the chassis. The airflowpassing through the flow path C is guided to the PFC power source board8 and the ballast power source board 10 by the intake force of the powersource cooling fan 17 or the exhaust fan 18 together with air present inthe chassis. The air that cooled the boards 8 and 10 is exhausted to theoutside of the chassis by the power source cooling fan 17 and theexhaust fan 18.

More detailed description of the configuration around the exhaust fan 18in the abovementioned cooling structure will be made with reference toFIGS. 1 and 2.

Heat-generating parts such as the lamp 1 in which the temperature of thereflector 2 increases up to near 500 degrees C. and plural electricalparts mounted on the PFC power source board 8 and ballast power sourceboard 10 are provided around the exhaust fan 18.

The lamp 1 is cooled with a cooling airflow (a first airflow) W1 that isflowed through the flow path B by the lamp cooling fan 14. A coolingairflow (the first airflow) W2 whose temperature is increased by drawingheat from the lamp 1 flows into the exhaust box 27 that forms an exhaustarea from the lamp 1 to the exhaust fan 18.

Then, the cooling airflow W2 is combined with a cooling airflow (a thirdairflow) W6 in the exhaust box 27 to form a cooling airflow W3, which isguided to the exhaust fan 18. The cooling airflow W6 will be describedlater.

Light emerging from the lamp 1 in its side direction may leak to theoutside of the projector through the opening of the exhaust fan 18. Tominimize such leak light, the first and second exhaust louvers(light-shielding members) 19 and 20 are provided in the exhaust box 27.

Each of the first exhaust louver 19 and the second exhaust louver 20 hasa structure which shields light from the lamp 1 but allows the passageof the cooling airflow.

The temperature of the cooling airflow W1 is strictly managed to assurea normal light-emitting mechanism of the lamp 1 such that, for example,the temperature at the top of the sphere portion of the light-emittingtube 41 may be equal to or lower than 1,000 degrees C. and that at thebottom thereof may be 900±20 degrees C. Therefore, to adequatelymaintain these temperatures, the cooling airflow W1 needs to have apredetermined direction and a predetermined volume (velocity).

The PFC power source board 8 is held by a power source cover 81, and theballast power source board 10 is held by a ballast cover 101. Thesecovers 81 and 101 are incorporated with each other to form a boxy powersource case E. The power source cover 81 and the ballast cover 101 havemultiple holes formed by punching.

A cooling airflow (a second airflow) W4 shown in the figures flows intothe power source case E through the holes formed thereon and cools theelectrical parts mounted on the PFC power source board 8 and ballastpower source board 10. Then, part of a cooling airflow (the secondairflow) W5 whose temperature is increased by drawing heat from theelectrical parts is guided to the exhaust fan 18.

In such a structure, the exhaust fan 18 takes in the cooling airflow W3from the flow path B and the cooling airflow W5 from the flow path A,and exhausts them to the outside of the chassis through the exhaust port24 a formed in the second side plate 24.

The reason for combining the cooling airflow W6 with the cooling airflowW2 in the exhaust box 27 will be described.

The first exhaust louver 19 and second exhaust louver 20 disposed in theexhaust box 27 are large resistance to the cooling airflow W2 thatcooled the lamp 1, which disturb the intake of the exhaust fan 18.

On the other hand, there is not anything which is large resistance tothe cooling airflow W5 that cooled the PFC power source board 8 andballast power source board 10.

Furthermore, the volume of the cooling airflow W1 which cools the lamp 1is limited by the abovementioned temperature management conditions.Therefore, if the cooling airflow W6 is not combined with the coolingairflow W2, the exhaust fan 18 mainly takes in the cooling airflow W5.

As a result, the velocity of the cooling airflow W5 is much larger thanthat of the cooling airflow W3 (cooling airflow W2), which increaseswind noise generated in the exhaust fan 18 to disturb reduction of noiseof the projector.

Therefore, in this embodiment, as is also shown in FIG. 2, an airflowopening 27 b as a third flow path is provided in the wall portion 27 aof the exhaust box 27. The wall portion partitions the exhaust area inthe flow path B from the flow path A. The airflow opening 27 bintroduces part W6 of the cooling airflow in the flow path A into theexhaust box 27.

Furthermore, an airflow opening 27 c as another third flow path isprovided near the exhaust fan 18 in the top face of the exhaust box 27to introduce part W6′ of the cooling airflow in the flow path A into theexhaust box 27.

Combining the cooling airflows W6 and W6′ with the cooling airflow W2makes it possible to increase the volume and velocity of the coolingairflow W3 which passes through inside the exhaust box 27 includinglarge resistance.

In addition, optimizing the size of the airflow openings 27 b and 27 cenables to reduce the velocity difference between the cooling airflowsW3 and W5 to a level at which generation of the wind noise in theexhaust fan 18 is suppressed.

Furthermore, distancing the combining point of the cooling airflows W3and W5 from the intake surface of the exhaust fan 18 reduces bias of thevolume of the cooling airflow introduced to the exhaust fan 18, therebyfurther decreasing noise.

Consequently, the airflow reaching the exhaust fan 18 becomessubstantially uniform at the intake surface thereof and the bias of theairflow velocity thereat is reduced. Thereby, the wind noise generatedwhen the blade of the exhaust fan 18 cuts across the airflows having avelocity difference can be reduced.

According to the inventor's experiment, in the case where the airflowopenings 27 b and 27 c were not provided in the exhaust box 27, thevelocity of the cooling airflow W5 was about 15 m/s, whereas thevelocity of the cooling airflow W3 was about 0.27 m/s. Therefore, thenoise level was high.

However, in the case where the airflow openings 27 b and 27 c wereprovided in the exhaust box 27, the velocity of the cooling airflow W5was about 1.5 m/s, whereas the velocity of the cooling airflow W3 wasabout 2.5 m/s. Thereby, the noise level reduced from 51.5 dB in theformer case to 48.3 dB in the latter case by 3.2 dB.

The noise reduction effect obtained by combining the cooling airflows W6and W6′ with the cooling airflow W2 was described thus far. Further, anadditional effect can also be obtained.

The heat value of the lamp 1 is larger than those of the PFC powersource board 8 and the ballast power source board 10. Accordingly, thetemperature of the cooling airflow W2 after cooling of the lamp 1 isinevitably increased. Therefore, if the cooling airflow W2 is directlyexhausted to the outside through the exhaust port 24 a of the secondside plate 24, the hot air may be blown to the user or the temperatureof the second side plate 24 may be increased.

However, exhausting the cooling airflow W3 produced by combining thecooling airflows W6 and W6′ having temperatures lower than that of thecooling airflow W2 with the cooling airflow W2 in the exhaust box 27 candecrease the exhaust temperature to solve the abovementioned problem. Inother words, this embodiment can achieve a low-noise projector capableof decreasing the temperatures of the exhaust air and the exteriormember.

The above embodiment described the case where an axial flow fan is usedas the exhaust fan 18. However, various fans such as a sirocco fan maybe used as the exhaust fan 18.

Embodiment 2

Next, description will be made of the cooling structure in a liquidcrystal projector that is Embodiment 2 of the present invention. As isunderstood from the experimental example described in Embodiment 1, thevelocity difference (bias) between the cooling airflows W3 and W5 stillremains even though the airflow openings 27 b and 27 c are provided inthe exhaust box 27.

Thus, in this embodiment, a flow-uniforming member F is provided betweenthe exhaust box 27 and the intake surface of the exhaust fan 18 as shownin FIG. 3.

The flow-uniforming member F is formed of a member having multiple holes(pores) such as a filter, a punching metal and a net. The shape andmaterial of the flow-uniforming member F are selected such that theintake resistance of the exhaust fan 18 is not excessively large.

The flow-uniforming member F can uniform the velocity of the two coolingairflows W3 and W5 that flow into the exhaust fan 18, thereby enablingto further reduce the wind noise generated in the exhaust fan 18.

According to the abovedescribed embodiments, in the case where theairflows are introduced to one fan from the first flow path for coolingthe light source and the second flow path for cooling the constituentparts other than the light source, the third airflow is first combinedwith the first airflow after it cooled the light source.

For cooling the light source (lamp) that requires a strict temperaturemanagement, an airflow velocity (volume) is set lower than that forcooling the other constituent parts. Therefore, the velocity of theoriginal first airflow is much lower than that of the second airflow.

However, combining the third airflow with the first airflow that cooledthe light source reduces the velocity difference between the combinedairflow immediately before it enters the fan and the second airflow. Inparticular, in the case where the light-shielding member that is largeresistance to the airflow is provided in the exhaust area, theabovementioned velocity difference can be reduced. Thereby, it ispossible to reduce the wind noise generated in the fan. Consequently, alow-noise image projection apparatus can be achieved.

Furthermore, combining the third airflow having a low temperature withthe first airflow having a high temperature due to cooling of the lightsource can decrease the exhaust temperature.

Although the preferred embodiments of the present invention weredescribed above, a transmissive liquid crystal panel and a digital micromirror device (DMD) can be used as the light modulation element. Inaddition, the cooling airflow W6 and W6′ can be directly introduced fromthe outside of the projector into the exhaust box 27.

Furthermore, the present invention is not limited to these preferredembodiments and various variations and modifications may be made withoutdeparting from the scope of the present invention.

This application claims foreign priority benefits based on JapanesePatent Application No. 2006-027728, filed on Feb. 3, 2006, which ishereby incorporated by reference herein in its entirety as if fully setforth herein.

1. An image projection apparatus configured to project an image usinglight from a light source, the apparatus comprising: a first flow pathconfigured to pass a first airflow for cooling the light source; asecond flow path configured to pass a second airflow for coolingconstituent parts other than the light source; an exhaust box includinga first opening, the first opening forming a third flow path configuredto pass a third airflow, and the exhaust box receiving the first airflowfrom the first flow path; and a fan configured to exhaust the secondairflow and combined airflow from the exhaust box, the combined airflowfrom the exhaust box including the first airflow and the third airflow,but not including the second airflow, which passes outside of theexhaust box to the fan, wherein the third airflow is derived from thesecond airflow that enters the second flow path, wherein the exhaust boxfurther includes a second opening, which forms a fourth flow pathconfigured to pass a fourth airflow for cooling the constituent partsother than the light source, wherein a first surface of the exhaust boxwhere the first opening is formed and a second surface of the exhaustbox where the second opening is formed face different directions,wherein the combined airflow from the exhaust box further includes thefourth airflow, and wherein the third airflow and the fourth airflow arederived from the second airflow that enters the second flow path.
 2. Theimage projection apparatus according to claim 1, wherein the first andsecond surfaces of the exhaust box are perpendicular to each other. 3.The image projection apparatus according to claim 1, wherein the firstopening and the second opening in the exhaust box have sizes configuredto cause a velocity difference between the second airflow and thecombined airflow to be at a level at which generation of wind noise inthe fan is suppressed.
 4. The image projection apparatus according toclaim 1, wherein the constituent parts other than the light sourceinclude at least one of electrical system parts for driving the lightsource and optical system parts which act on the light introduced fromthe light source to a projection optical system.
 5. The image projectionapparatus according to claim 1, wherein the fan is an axial flow fan. 6.The image projection apparatus according to claim 1, wherein the thirdairflow is exhausted to the outside by the fan, without cooling thelight source.
 7. An image display system comprising: an image projectionapparatus; and an image supply apparatus configured to supply imageinformation to the image projection apparatus, wherein the imageprojection apparatus is configured to project an image based on theimage information using light from a light source, the image projectionapparatus comprising: a first flow path configured to pass a firstairflow for cooling the light source; a second flow path configured topass a second airflow for cooling constituent parts other than the lightsource; an exhaust box including a first opening, the first openingforming a third flow path configured to pass a third airflow, and theexhaust box receiving the first airflow from the first flow path; and afan configured to exhaust the second airflow and combined airflow fromthe exhaust box, the combined airflow from the exhaust box including thefirst airflow and the third airflow, but not including the secondairflow, which passes outside of the exhaust box to the fan, wherein thethird airflow is derived from the second airflow that enters the secondflow path, wherein the exhaust box further includes a second opening,which forms a fourth flow path configured to pass a fourth airflow forcooling the constituent parts other than the light source, wherein afirst surface of the exhaust box where the first opening is formed and asecond surface of the exhaust box where the second opening is formedface different directions, wherein the combined airflow from the exhaustbox further includes the fourth airflow, and wherein the third airflowand the fourth airflow are derived from the second airflow that entersthe second flow path.